1. Field of the Invention
This invention relates to supports for dominance deficiencies of the big toe, and particularly to demi pointe equalizer, exerciser, and tensioning compensation devices for varum and length dominance deficiencies of the big toe.
2. Description of Related Art
Normal walking consists of two distinct phases: the stance phase and the swing phase. The stance phase can be divided into three parts: 1) contact, 2) midstance, and 3) propulsion. When one limb is beginning the stance phase, the other is concluding stance and beginning the swing phase. For years, it was thought that the foot moved down, or planterflexed, to propel us forward. The foot was then thought to be acting as a lever arm, similar to the way a crow bar works. When viewed in terms of the body as a whole, however, it is actually too small to do that effectively.
In reality, it is the hallux complex, foot, leg and thigh that act as the lever from the hip, not the foot alone from the ankle. Using the length provided between the hip and demipointe (hallux complex), we can create a lever effect against the ground, forcing the ground behind us. Since the ground does not move, we instead cause an advance in the forward direction with both the center of gravity located within the head and the center of mass located within the body. The integrated action of these two separate centers, the center of gravity and the center of mass are important to distinguish as being location specific when discussing postural motion. Since the foot is in contact with the ground, its purpose is to create the maximum amount of longitudinal shear, or backwards thrust necessary to push us forward, while coordinating with the body posture to maintain a stabilized and oriented cranium. To accomplish this, the foot undergoes two basic opposing motions. The first motion is supination. Supination prepares the involved musculature for the action of a shock absorbing "lengthening contraction" during the initial pronation interval of contact in the support phase.
Supination is a triplaner motion that occurs on all three cardinal planes of the body. These are called the Frontal, Saggital, and Transverse Planes. The motions that occur are Inversion, Planterflexion, and Adduction and reactively take place at the Subtalar Joint as it acts in concert with an ipsilateral turning out of the hip. The Subtalar Joint is located beneath the ankle joint at the interface of the Talus and the Calcaneous and is made up of three articular facets. These facets allow for freedom in this three-way movement, which allows for active shock absorption during the driving or power segment from midstance to push off. This motion also allows for the foot to be extremely stable under weight bearing conditions as the axis of the rear foot joint (subtalar joint) becomes perpendicular to the axis of the midfoot (midtarsal joint). This perpendicular joint buttress arrangement allows for the stability on the part of the medial longitudinal arch, as held together-congruent with the windlass effected plantar ligament (described by Hicks). The foot undergoes this supinatory motion from the end of the propulsion phase of gait through the swing phase and returns to the fully supinated position so that at contact, it can go through the opposite motion of pronation.
Pronation, like supination, is a triplaner motion reactively taking place at the Subtalar joint in conjunction with a turning in at the hip. Its direction of movement is opposite of supination and is comprised of Eversion, Planterflexion, and Abduction occurring on the same cardinal planes. A muscular lengthening contraction resistance allows the subtalar joint motion of pronation to absorb the shock of the heel strike while dampening the deceleration stress of the body mass acting on the foot and lower limb. This deceleration occurs as the foot follows through to the hallux complex grounding at midstance. Corrected timing of hallux grounding at midstance provides for an increased amount of power and shock absorption to be derived from the medial longitudinal arch. The hallux complex is the grounding buttress for the medial longitudinal arch. The hallux complex acts as vertical posture support stop and as a triggered launching platform. As the hallux dorsiflexes, it creates a lengthening, strengthening and tensioning of structures in preparation for the release of energies during the propulsion phase achieved by the push off of the big toe (hallux). This description of pronation assists in explaining greater energy output and shock absorption. The increase in shock absorption is capable of reducing the stress fracture and shin splint incidence seen with athletes during running and jumping activities. Additionally, the vertical support of the hallux complex immediately lessens the reactive check reining and foreshortening of the posterior postural chain musculature, see, FIG. 1. The posterior chain muscles include the hamstring, calf, peroneus, and foot flexors.
Walking speed propulsion is initiated in the toes by first contacting the ground at the fifth metatarsal and then pronating the foot along the line of the metatarsals and toes as they contact and leave the ground, ending with the big toe complex, which then pushes off at the end of the step. In contrast, if we look at the situation of the hallux complex not being fully grounded in neutral position (midstance), the musculature is found to be in a rigid, braced, shortened condition as an attempt to ground the body posture at midstance. In doing so, some or most of our propulsion phase ability to power, resist and absorb shock from ground force opposition is lost. The hallux complex if properly grounded in time and motion, fully activates the medial longitudinal arch mechanics to create a complete propelling thrust, as well as the protective shock absorption for the dependent body structures.
In many people, however, the foot is not constructed ideally. This flaw is inadequate length and grounding tension of the hallux complex, making it impossible to coordinate its axial support postural requirements during a time motion sequence. In cases where the first metatarsal bone is short, or functionally required to be on an elevated plane above the rest of the foot for working efficiency, the pronation described above does not end with the big toe making contact with the ground in a normal way. Such conditions lead to sagittal motion forefoot roll over linear instability. The result is that the lifting and balancing efforts with the ground are not structurally coordinated with the rest of the foot in holding axial posture. This leads to eventual posture collapse and weakness as the compensating musculature tires at holding correct structural alignment geometry. FIGS. 2 and 3 show a normal foot and a foot with a short first metatarsal bone. These figures also show the roll over leverage points used in the push off of a step. FIG. 2 shows a normal skeletal view of a foot 1. Clearly, when the first metatarsal bone 2 is ahead of or equal to the second metatarsal bone 3 the leverage is straight across the joints as shown. This is shown by the dashed line that shows the proper alignment of the metatarsal joints. FIG. 3 shows a skeletal view of a foot 4 where the leverage points are not properly aligned. Here, the first metatarsal bone 5 is short as compared to a normal foot (e.g., that of FIG. 2). As shown by the two dashed lines in this figure, the end of the first metatarsal bone 5 does not align with the end of the second metatarsal bone 3. This misalignment forces a patient to muscle brace (muscle compensate) and or over pronate (i.e., roll the foot excessively inward) while toeing out in an attempt to allow the big toe to make contact with the ground for the push off. This geometric cascade side loads the knee inward, and produces a counter rotation sheer within the knee joint, and causes other reactive physical problems throughout the kinetic centers of posture.
The kinetic centers of posture collectively have, as a primary survival function purpose, the work of maintaining a stable and oriented cranium. Instability and disorientation are the consequences of losing cranial position during any activity. When viewed in this manner, the cranium is to be considered the upper terminus of the body's postural kinetic chain, which has a corresponding lower terminus at the Demi Pointe support area of the hallux complex. See, FIG. 1.
To address the problems just discussed, several inventions have been developed. These devices address the varum forefoot deformity by attempting to "post" (or to lift and support) the mid and forefoot. These devices tend to support the first and second or even the first, second and third metatarsals. For example, U.S. Pat. No. 5,327,664 to Rothbart teaches a foot orthotic with a forefoot posting shim. The shim is designed to lift the first through third metatarsals on a sloped support. However, for the comfort of the patient, this device is designed to extend only as far as the one-five metatarsal parabola.
U.S. Pat. No. 5,327,663 to Pryce discloses a corrective foot insole for treating a condition known as flexible flat foot. This device has two primary components. First, there is a forefoot portion that provides lift for the two interior toes that runs back almost to the heel. The second component is a support arch that provides additional lift for the metatarsal. The support arch rests on the forefoot portion. Although the Pryce device addresses the problem of the flexible flat foot, it cannot solve the problems of a differentially short and or functionally elevated first metatarsal bone because it provides support for more than just the big toe. Supporting more than just the big toe cannot solve the problem because the support maintains the misalignment between the first and second metatarsal bones (as it does not recognize that the hallux, like the thumb, operates on a different geometric plane than the other digit complexes, which function on a collective plane). As a result, uncoordinated pronation, in an attempt to load the big toe for support and balance of axial posture, becomes even more pronounced and body weight leverages off the second toe complex to an even greater extent.
Finally, these devices are bulky in design, which often causes problems with stock shoes. It is also not practical to combine or substitute them with shoe manufacturer's standard inserts.